This invention relates to processes of preparing fibers useful in forming composite articles. More particularly, this invention relates to carbon fiber-containing fiber blends which are useful in preparing composite articles.
Carbon fiber-containing tapes and rovings have been known for several years. See, for example, U.S. Pat. Nos. 3,704,485, 3,873,389, and 3,795,944, as well as U.S. Pat. Nos. 3,993,726 and 3,728,424.
Also it is known to intermix two similar or different types of fibers, particularly to obtain high bulk. See for example, U.S. Pat. Nos. 4,219,997, 4,218,869, 3,959,962, 3,968,638 and 3,958,310. And the combining of different types of fibers has been facilitated using various types of fluid jets. See, e.g., the ""310 patent and U.S. Pat. No. 4,147,020. However, in the ""020 patent, after combining the yarns are cut into short lengths.
U.S. Pat. No. 4,226,079, issued Oct. 7, 1980, discloses the combining of two different types of fibers, in order to produce a bulk yarn. The fibers are intermixed in a jet intermixing zone. However, the fibers disclosed in the patent are polyester and polyamid. No disclosure is made of the combining of carbon the thermoplastic fibers.
U.S. Pat. No. 3,175,351 discloses a method of bulking continuous filament yarns. In addition, it is disclosed that the two yarns which are combined may be of different compositions. However, none of the compositions is a carbon fiber.
U.S. Pat. No. 3,859,158 discloses the preparation of carbon fiber reinforced composite articles by forming an open weave of a carbon fiber and coating with a carbonaceous material. U.S. Pat. No. 4,368,234 discloses complex woven materials used for reinforcement which are formed from alternating bands of graphite fibers and low modulus fibers. However, the woven materials disclosed in this patent are subsequently impregnated with a thermosetting resin and cured.
Commonly assigned U.S. Pat. No. 4,479,999 to Buckley and McMahon, discloses an improved woven fabric comprised of fusible and infusible fibers wherein the infusible fibers include graphite or carbon fibers, and the fusible fibers are thermoplastic in nature. According to the patent, fusible and infusible fibers are woven into a fabric and thermally bonded together by heating above the melting point of the fusible fiber. This patent application does not disclose, however, the preparation of linearly intermixed fiber tow products or that such products are useful in forming composite articles. The patent application also does not disclose the preparation of such materials using a gas jet intermixing means.
In the prior art, there were two distinct methods of forming carbon fiber-containing composites. The first and older method involved simply forming a tape or fabric prepreg by painting or coating carbon fiber tows or fabric with a solution and/or low viscosity melt of a thermosetting material which was then cured. The second process involved the extrusion of carbon fiber tapes impregnated with high melting, thermoplastic polymers. These tapes or fabrics were then used in forming the composite. However, the prepregs formed by both of these processes were somewhat difficult to handle. Specifically, prior art thermoplastic tapes were stiff and xe2x80x9cboardyxe2x80x9d and could not be draped across intricately shaped molds. While thermoset prepregs were somewhat more flexible, they were often quite tacky and difficult to handle. As a result, the use of both types of tapes was limited.
Accordingly, it is an object of this invention to prepare fibrous blends which are useful in forming thermoplastic carbon fiber composites.
It is another object of this invention to prepare materials, e.g., fabrics, which may be formed into fiber composites.
These and other objectives are obtained by employing the process of the instant invention.
Basically, the process of this invention involves (a) forming a carbon fiber tow from a multitude of carbon fibers; (b) forming a thermoplastic polymeric fiber tow; (c) intermixing the two tows; and (d) withdrawing the intermixed tows for use. The intermixed tows may then be employed in forming various carbon fiber-containing composites.
The fiber blends prepared according to the instant invention are flexible and handleable and have good draping properties, so that they can be used to form intricately shaped articles. In addition, because of the intermixing of the two fibers, good wetting of the carbon fiber by the thermoplastic material is obtained when appropriate heat and pressure are applied to the mold. Good wetting is obtained in large measure because of the substantially uniform distribution of the thermoplastic fiber and the carbon fiber within the fiber blend. Specifically, the products of the instant invention find particular utility in end use applications where a small radius of curvature in the final product is desired. For example, using the prior art tapes, it was not possible in many instances to prepare articles which had 90xc2x0 bend, because the tapes would crack or deform at the bend line. However, the processes of the instant invention may be employed with radii of curvature as low as 0.002 in.